1. Field of the Invention
The present invention relates generally to large diameter pneumatic percussive hammers and more particularly to large drill bit assemblies with removable bit of the drill bit assembly.
2. Description of Related Art
It is known that the bit head of any drill bit assembly typically wears faster than a shank due to the aggressive environmental conditions at the working end of the drill bit assembly. Some drill bit assemblies are completely discarded even when the shank of the drill bit assembly is still operable. This is due to the fact that the bit head portion of the drill bit assembly is worn so severely that the bit head cannot be reconditioned back into working order.
It is well known historically that regular replacement of the bit head of the drill bit assembly, dressing of the bit assembly cutting elements in the bit head, or replacement of the entire drill bit would greatly increase the overall productivity of the drilling system. It is also well known that maintaining or replacing the entire drill bit assembly can be quite costly to the overall operation. The existing methods for replacing or redressing of the worn drill bit heads for large class drilling machines is expensive, labor intensive, and sometimes dangerous depending on the equipment utilized to perform the task. Dressing the cutting elements in a drill bit can be very labor intensive and in some cases cannot be done adequately enough at the jobsite, once again adding to the overall cost of the operation.
Therefore, every effort is taken to balance the necessity to keep the drill bit drilling effectively and at the same time attempts are made to reduce the cost of the operation by keeping the drill bit in service as long as possible. The intention of the bit head replacement is to keep the bit head of the drill bit assembly as effective as possible during its operation, but minimizing the cost of the drill bit assembly by making interchange of the bit head of the drill bit assembly simple, and with minimal labor time.
Also well known is the fact that large drill bit assemblies are more costly due to the specific machinery needed to manufacture such large drill bit assemblies and the necessity for costly large steel forgings to be provided. All of these points and the limited market size to sell such product to, drives the cost of these particularly large drill bit assemblies into a higher, sometimes unaffordable cost condition for most drilling operations of that size, unless no other means for drilling the earth formation is found suitable.
Many designs exist for attempting to replace the bit head of the drill bit assembly, but primarily have been focused on smaller drill bit assemblies, and the necessity to drag steel casing into the drilled hole behind the bit assembly.
U.S. Pat. No. 1,995,043 to Ray R. Sanderson shows the replacement of the cutting elements used in churn or percussion drilling. The forward working portion of the bit assembly is replaceable when worn.
U.S. Pat. Nos. 3,152,654 & 3,260,319 to Robert E. Conover shows percussion style drill bits with replacement sections that have been retained in position by solid retention pins and roll pins.
U.S. Pat. No. 4,051,912 to Kenneth M. White shows a bit assembly with a replaceable forward working section that is threaded and wedged together.
U.S. Pat. No. 4,083,415 to John F. Kita et al. shows a bit assembly with a replaceable forward working section that is affixed by means of steel balls secured by threaded plugs.
U.S. Pat. No. 4,085,809 to Robert Lovell et al. shows a drill bit assembly with a replaceable bit head and parts thereof that are assembled using a threaded design.
U.S. Pat. No. 4,466,498 to Allen E. Bardwell shows a drill bit assembly with replaceable bit heads that are affixed with the utilization of bolts or threaded fasteners.
U.S. Pat. No. 4,919,221 to Jack H. Pascale shows a drill bit assembly with a replaceable bit head that is attached and retained by a drive spline helix locking means.
U.S. Pat. No. 5,113,594 to Yoshimi Ishihara et al. & U.S. Pat. No. 5,139,099 to Takeshi Hayashi et al. show drill bit assemblies comprising of replaceable bit heads of the drill bit assembly but affixed in a fashion where the bit heads are capable of rotating within.
U.S. Pat. No. 6,021,856 to Jack H. Pascale shows a drill bit assembly with a replaceable bit head that is held in place by ring segments.
U.S. Pat. Nos. 5,787,999 & 5,975,222 to Adris L. Holte shows a drill bit assembly with replaceable retracting and extending arms used in the under-reaming system.
None of the prior art patents listed above or known contain consideration for rotationally driving the bit head with a set of lugs and retaining the bit head in the drill bit assembly by means of solid retaining members kept in place with roll pins for easy bit head removal and installation. Furthermore, several of the above mentioned patents attempt to rigidly affix the bit head of the drill bit assembly to the shank for percussive force energy transmission, which inherently has been found to limit the life expectancy of the retaining members. Furthermore, none of the above mentioned patents make mention or attempt to separate the drilling forces to better design force carrying members more suited for the application.